The invention is particularly concerned with products and their derivatives obtained by the hydroformylation of C4 feeds comprising a mixture of isobutylene and at least one normal butene, and optionally other C4 components such as butane.
In this invention, the term butene or butylene generically refers to all hydrocarbon compounds having 4 carbons and at least one unsaturated bond that bonds together two carbons. Examples of specific butenes include, but are not limited to, butene-1, butene-2 (which refers to the combination of the cis and trans forms), isobutene or isobutylene, and butadiene. Thus, the generic term butene or butylene refers to the combination of all types of specific butene compounds.
Butene streams are used as raw materials for hydroformylation to produce valeraldehyde. In some commercial operations valeraldehyde is then dimerised and the product of dimerisation hydrogenated to produce 2 propyl heptanol or mixtures thereof with other alcohols which are finding use as alcohols in esterification reactions to produce plasticiser esters. Alternatively valeraldehyde may be hydrogenated to produce pentanol or amyl alcohol or mixtures of different isomers thereof which may be used as a solvent or in the production of materials such as zinc dialkyl dithiophosphates. The valeraldehyde may also be oxidised to produce valeric acid or isomer mixtures thereof which may be used in synthetic ester lubricant production.
Butenes have generally been obtained from C4 cuts that are obtained from steam cracking and catalytic cracking refinery processes. These cuts typically contain a mixture of C4 saturated and unsaturated materials including butadiene, normal butenes including both butene-1 and butene-2, of which both the cis- and the trans-form typically occur, and isobutylene. The butadiene may be removed by extraction or reaction, or converted by selective hydrogenation to produce a stream which contains predominantly normal butenes and isobutylene; such a stream is sometimes known as raffinate-1. The composition of such a stream in terms of the different hydrocarbon molecules may be determined by using conventional gas chromatographic techniques.
More recently butene streams have become available from an olefin stream obtained from an oxygenate conversion reaction. Such a butene stream is characterized by having a high butene content, but is low in components that can act as catalyst poisons. Although the butene components generally include a relatively high concentration of the more undesirable butene-2 and isobutylene compounds, we have found that the stream can be hydroformylated to convert a significantly high portion of those components to aldehyde products, which may then be further reacted in the manner described above.
Oxygenates used as feed to, or formed during, the oxygenate conversion to olefins process, can be present in the butene stream. Such components will not significantly affect the hydroformylation process, nor significantly affect the resulting aldehyde or aldehyde derivative products.
In one embodiment of this invention, the butene stream used in the invention is separated from an olefin stream that is obtained by contacting oxygenate with an olefin forming catalyst. The oxygenate comprises at least one organic compound containing at least one oxygen atom. Non-limiting examples include aliphatic alcohols, ethers, carbonyl compounds (aldehydes, ketones, carboxylic acids, carbonates, esters and the like). When the oxygenate is an alcohol, the alcohol can include an aliphatic moiety having from 1 to 10 carbon atoms, more preferably from 1 to 4 carbon atoms. Representative alcohols include but are not necessarily limited to lower straight and branched chain aliphatic alcohols and their unsaturated counterparts. Examples of suitable oxygenate compounds include, but are not limited to: methanol; ethanol; n-propanol; isopropanol; C4-C20 alcohols; methyl ethyl ether; dimethyl ether; diethyl ether; di-isopropyl ether; formaldehyde; dimethyl carbonate; dimethyl ketone; acetic acid; and mixtures thereof. Preferred oxygenate compounds are methanol, dimethyl ether, or a mixture thereof.
U.S. Pat. Nos. 6,770,791 and 6,784,330 describe how butene feeds for use in this invention may be obtained by the conversion of an oxygenate.
It may be desirable to increase the ethylene yield in the oxygenate to olefin process, since ethylene is typically of greater commercial value than other olefins produced in the process. One way of increasing the ethylene yield in the oxygenate to olefin process is to operate the process such that there is less than 100% conversion of oxygenate to olefin product. This means that not all of the oxygenate feed will be completely converted to olefin or some other final non-water product. Less than 100% conversion can also mean that some of the oxygenate feed is not converted, or that not all intermediate products are completely converted to olefin. For example, dimethyl ether can be used as a feed or it may form as an intermediate product in the conversion to olefin. Therefore, the presence of dimethyl ether in the olefin product will generally imply that the conversion of oxygenate to olefin is less than 100%. By the same manner, other oxygenates, such as acetaldehyde, may be present, also indicating less than 100% conversion of feed or intermediate products.
In order to obtain the butene feeds from olefins produced from oxygenates for use in this invention, it is desirable to separate a butene rich stream from the olefin product stream produced in the oxygenate to olefin process. Although it is preferred to obtain a butene rich stream that is low in oxygenate concentration, this invention provides the advantage that a high degree of separation of non-butene compounds is not necessary. For example, propylene and pentene can be relatively easily removed from butene. Dimethyl ether, which may be present in the olefin product stream in rather large quantities at less than complete conversion, will tend to separate with the propylene rich stream. Although some oxygenate contaminants, particularly acetaldehyde, are likely to be present in the separated butylene stream, little if any oxygenate removal would be required to use the stream in further derivative processing if certain processes are used. According to this invention, it is desirable to use a rhodium hydroformylation catalyst for derivative processing of the separated butylene stream, because little to no pretreatment of the butylene stream for oxygenate removal would be required. Such catalyst is particularly suited to tolerate relatively high levels of acetaldehyde.
Separation can be accomplished using conventional means. Conventional distillation techniques are preferred.
It is known that within butene mixtures the different butene species have a different reactivity in hydroformylation reactions. For instance when using a rhodium catalyst in conjunction with a phosphine ligand such as triphenyl phosphine, butene-1 is considerably more reactive than butene-2 which has been more reactive than isobutylene. In addition it is known that the different pentanals produced by the hydroformylation of mixed butene feeds have different reactivities in subsequent aldolisation reactions with normal pentanal being considerably more reactive than 2-methyl butanal and accordingly various attempts have been made to keep the ratio of normal pentanal to 2-methyl butanal (sometimes known as the normal-to-iso ratio) as high as possible, such as is described in U.S. Pat. No. 4,426,542. 3 methyl butanal which is produced by the hydroformylation of isobutylene is however more reactive than 2 methyl butanal in aldol reactions but is difficult to produce from a butene mixture due to its lack of reactivity in rhodium catalysed hydroformylation.
During the hydroformylation of mixed butene feeds containing 1 butene and cis- and trans-2-butene, these materials will convert to a mixture of normal valeraldehyde and 2 methyl butyraldehyde. In order to enhance the reactivity and usefulness of the aldehyde it is desirable to increase the proportion of the normal valeraldehyde that is present, and when a rhodium catalyst is employed, this can be influenced by the choice of the ligand used in conjunction with the rhodium.
Isobutylene or isobutene is not considered to be generally reactive in rhodium catalysed hydroformylation and has generally been removed prior to hydroformylation. However when subject to hydroformylation, isobutylene is known to produce 3 methyl butyraldehyde at low conversion.
It is also known that mixed butene feeds containing isobutylene can be hydroformylated (including the hydroformylation of the isobutylene) by the use of a cobalt catalyst system. However such a system results in considerable isomerisation resulting in a high selectivity of normal butenes to the less desired 2-methyl butanal, and in hydrogenation resulting in the formation of considerable amounts of C5 alcohols which cannot then be used in subsequent aldolisation reactions.
U.S. Pat. No. 4,969,953 illustrates the hydroformylation of mixed butene feeds containing isobutylene using a rhodium catalyst in conjunction with a triphenyl phosphine ligand and states that the reaction speed of each component of butenes is different. Examples 1 and 2 use a feed containing 4% isobutylene, Example 1 achieves a 26% conversion of isobutylene resulting in a composition having a normal-to-iso ratio of 10 and a ratio of 3 methyl butanal to 2 methyl butanal of only 0.2; Example 2 employs higher pressures and obtains a higher conversion of both isobutylene and butene-2 to produce a pentanal mixture in which the ratio of 3 methyl butanal to 2 methyl butanal is again 0.2. Example 3 employs a mixed butene feed containing 51.5% isobutylene at the lower pressure and obtains a 2.3% conversion of isobutylene to produce a pentanal mixture containing 3 methyl-butanal and 2 methyl-butanal in a ratio of only 0.1.
U.S. Pat. No. 6,100,432 shows the separation of isobutylene from raffinate-1, producing a raffinate-2, prior to hydroformylation with a rhodium catalyst. U.S. Pat. No. 4,287,370 states that the C4 feed to hydroformylation should contain no more than 1 wt % isobutylene. Similarly US Publication 2003/0022947 A1 discloses hydroformylation of raffinate-2, an isobutene depleted stream said to contain no more than 5 mol % isobutene. In this patent application, only the butene-1 is hydroformylated, the butene-2 and the isobutylene being substantially unreacted. An article by Walter J Scheidmeir of BASF in Chemiker-Zeitung 96 Jahrgang (1972) Nr 7. pp 383-387 shows the hydroformylation of a butene stream containing significant amounts of isobutylene (i.e. 46%) in which most of the unsaturated materials including the isobutylene, are converted. In this case, it is clear that cobalt salts were used as the hydroformylation catalyst, as evidenced by the high selectivity to alcohols in the product composition as well as the high yield of dimethylpropanal and dimethylpropanol that are reported, a combination of features that is typical for a high pressure cobalt based catalyst system, and atypical for the low pressure rhodium and phosphorus liganded catalyst systems. The product mix, excluding heavies, was reported to contain as much as 39.6%, presumably by weight, of various C5 alcohol isomers, and respectively 1.2% and 4.1% of dimethylpropanal and dimethylpropanol. U.S. Pat. No. 6,555,716 describes a process in which raffinate-1 is fed to a hydroformylation reactor that employs a rhodium catalyst with a two phase aqueous system using a water soluble ligand, i.e. trisulphonated triphenylphosphine. However, far from all the isobutylene is converted, the highest conversion of isobutylene being 13.6% in Example 13. Furthermore the yield in this reaction is low and high catalyst recycle volumes are required, giving the process as described a low effectivity and a low efficiency.